1. Field of the Invention
The present invention relates to a plastic lens having a photochromic layer and a manufacturing method thereof. Particularly, the present invention relates to a plastic lens having a photochromic layer which exhibits excellent photochromic properties.
2. Description of the Related Art
Photochromism is a phenomenon exhibited by a compound which reversibly changes color when exposed to light containing ultraviolet rays such as sunlight, and returns to its original color (colorless state) when the ultraviolet radiation is discontinued.
Photochromic properties are beneficial in manufacturing plastic spectacle lenses.
The following three methods, for example, are proposed to be used to manufacture a plastic spectacle lens having photochromic properties.
The first method is to impregnate a photochromic compound into surface of a lens having no photochromic properties.
The second method is to form a primer layer having photochromic properties and a hard coat layer on the surface of a lens by coating.
The third method is to dissolve a photochromic compound into a monomer, and then polymerize the monomer to directly obtain a photochromic lens.
Particularly, since the second method (i.e., the coating method) can be applied to various existing plastic lenses, it has been receiving wide attention recently (see, for example, International Publication No. WO03/011967).
International Publication No. WO03/011967 discloses a method in which a material obtained by dissolving a photochromic compound into a radical polymerizable monomer is coated on the surface of a lens, and then the coated material is cured by ultraviolet radiation.
This method is effective because it can also be applied to recently-developed high refractive index materials.